Energy storage system

ABSTRACT

Systems and methods for controlling power flow to and from an energy storage system are provided. One energy storage system includes an energy storage device and a bidirectional inverter configured to control a flow of power into or out of the energy storage device via a plurality of phases. The energy storage system further includes a controller configured to control the bidirectional inverter based on a load condition on one or more phases. The controller is configured to control the bidirectional inverter to store power generated by a generator set in the energy storage device and transmit power from the energy storage device to a load driven by the generator set in response to detecting a load imbalance between the phases.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/626,190, filed Feb. 19, 2015, to issue as U.S. Pat. No.9,780,567. The content of this application is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to the field of generators.More particularly, the present disclosure relates to systems and methodsfor controlling operation of an energy storage system configured to becoupled to one or more generator sets.

BACKGROUND

Generator sets can be used to power a wide variety of loads. Varyingloads can be powered by one or more generator sets by increasing ordecreasing a power output of the generator sets to meet load demand.However, if widely varying loads are connected to the generator sets,the size of the generator sets may be larger than needed to addressordinary load demand in order to meet occasional large demand.Additionally, variations in load demand or phase imbalances may causethe generator sets to operate inefficiently.

SUMMARY

One embodiment of the disclosure relates to an energy storage system.The energy storage system includes an energy storage device and abidirectional inverter configured to control a flow of power into or outof the energy storage device. The energy storage system further includesa controller configured to control the bidirectional inverter based onone or more signals (e.g., digital or analog signals) received from agenerator set coupled to the bidirectional inverter via an alternatingcurrent (AC) bus. The controller is configured to, based on the one ormore signals, control the bidirectional inverter to store powergenerated by the generator set in the energy storage device and transmitpower from the energy storage device to a load driven by the generatorset to maintain the generator set within a range of one or moreoperating conditions.

Another embodiment relates to a method of controlling a flow of power toand from an energy storage system. The method includes receiving, at acontroller of the energy storage system, one or more signals from agenerator set. The method further includes monitoring, at thecontroller, one or more operating conditions of the generator set basedon the one or more signals. The method further includes controlling abidirectional inverter of the energy storage system to store powergenerated by the generator set in an energy storage device of the energystorage system and transmit power from the energy storage device to aload driven by the generator set to maintain the generator set within arange of one or more operating conditions. The bidirectional inverter ofthe energy storage system may be coupled to the generator set by an ACbus.

Another embodiment relates to a hybrid generator system including agenerator set configured to generate power to drive a load via an ACbus. The hybrid generator system further includes an energy storagesystem including an energy storage device and a bidirectional invertercoupled in parallel to the generator set on the AC bus and configured tocontrol a flow of power into or out of the energy storage device. Theenergy storage system further includes a controller configured tocontrol the bidirectional inverter based on one or more signals receivedfrom the generator set. The controller is configured to, based on theone or more signals, control the bidirectional inverter to store powergenerated by the generator set in the energy storage device and transmitpower from the energy storage device to a load driven by the generatorset to maintain the generator set within a range of one or moreoperating conditions.

Another embodiment relates to an energy storage system including anenergy storage device and a bidirectional inverter configured to controla flow of power into or out of the energy storage device via a pluralityof phases. The energy storage system further includes a controllerconfigured to control the bidirectional inverter based on a loadcondition on one or more of the plurality of phases. The controller isconfigured to control the bidirectional inverter to store powergenerated by a generator set in the energy storage device and transmitpower from the energy storage device to a load driven by the generatorset in response to detecting a load imbalance between the plurality ofphases.

Another embodiment relates to a method of controlling a flow of power toand from an energy storage system. The method includes determining, at acontroller of the energy storage system, a load condition on one or moreof a plurality of phases of a local AC grid. The method further includescontrolling a bidirectional inverter of the energy storage system tostore power from the local AC grid in an energy storage device of theenergy storage system and transmit power from the energy storage deviceto a load driven by the local AC grid in response to detecting a loadimbalance between the plurality of phases.

Another embodiment relates to a hybrid generator system including agenerator set configured to generate power to drive a load and an energystorage system. The energy storage system includes an energy storagedevice and a bidirectional inverter configured to control a flow ofpower into or out of the energy storage device via a plurality ofphases. The energy storage system further includes a controllerconfigured to control the bidirectional inverter based on a loadcondition on one or more of the plurality of phases. The controller isconfigured to control the bidirectional inverter to store powergenerated by the generator set in the energy storage device and transmitpower from the energy storage device to the load in response todetecting a load imbalance between the plurality of phases.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements, inwhich:

FIG. 1 is a block diagram illustrating a hybrid generator systemaccording to an exemplary embodiment;

FIG. 2 is a detailed exemplary implementation of the energy storagesystem of FIG. 1;

FIG. 3 is a flow diagram of a process for controlling an energy storagesystem according to an exemplary embodiment;

FIG. 4 is a state diagram of an energy storage system control schemeaccording to an exemplary embodiment;

FIG. 5 is a flow diagram of a process for controlling network powerusing an energy storage system according to an exemplary embodiment; and

FIG. 6 is a flow diagram of a process for controlling transients usingan energy storage system according to an exemplary embodiment.

FIG. 7 is a block diagram of a hybrid generator system according toanother exemplary embodiment; and

FIG. 8 is a flow diagram of a process for controlling an energy storagesystem to balance load across multiple phases according to an exemplaryembodiment.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplaryembodiments in detail, it should be understood that the application isnot limited to the details or methodology set forth in the descriptionor illustrated in the figures. It should also be understood that theterminology is for the purpose of description only and should not beregarded as limiting.

Referring generally to the figures, systems and methods that may be usedto power loads in conjunction with generators are provided according toexemplary embodiments. Generator sets, or gensets, are used to providepower to one or more loads, such as a local power network or grid (e.g.,a power grid powering a location, such as a building, room or group ofrooms, etc.). The power demands of the loads may vary with changingconditions, such as increasing and decreasing draw on the local grid. Toaddress the changing load demand, gensets may increase or decrease theoutput power generated by the gensets, such as increasing power outputwith increased load, or decreasing the power output with decreased powerdemand. As a result, the gensets may operate outside of a preferredrange of operating conditions (e.g., a range of operating conditionsassociated with efficient, such as fuel-efficient, operation of thegenset) for at least a portion of time during which changes in demandare addressed. For example, increasing or decreasing an operatingcondition, such as a rotational velocity for a variable speed genset(e.g., rotations per minute, or RPM), of the engine of a genset, orincreasing torque output for a fixed speed synchronous genset, may causethe engine to operate in a manner that utilizes fuel at a higher ratethan in a preferred range of rotational velocities. Additionally, loadtransients due to changing load demand can affect quality of the powerprovided by the gensets (e.g., cause a voltage provided by the gensetsto temporarily drop or spike) requiring gensets to react quickly to loadchanges or operate with excess power output capacity available as a“spinning reserve” for potential sudden demand increases.

The present disclosure provides exemplary systems and methods forutilizing an energy storage system that can be coupled to one or moregensets to help provide power to one or more loads in an AC paralleledhybrid configuration. An exemplary energy storage system includes anenergy storage device (e.g., one or more batteries, capacitors orcapacitor banks, etc.) and an inverter configured to control flow ofpower to and from the energy storage device. The inverter may be abidirectional inverter configured to bi-directionally transmit powerbetween the energy storage device and one or more generator sets coupledto the inverter (e.g., an output of the one or more generator sets). Theinverter includes a controller configured to control operation of thebidirectional inverter. In some embodiments, the controller controls theinverter based on one or more digital or analog signals received fromthe genset(s). The signal(s) may be indicative of or provide informationrelating to one or more operating conditions of the genset(s). Theenergy storage system may control the inverter to storage power (e.g.,excess power) generated by the genset(s) in the energy storage deviceand/or transmit power stored in the energy storage device to the load(s)based on the signal(s) and/or operating condition(s).

In some embodiments, the AC paralleled energy storage system may controlthe inverter to maintain one or more of the gensets within a range ofoperating conditions, such as a range associated with efficient (e.g.,fuel-efficient) operation of the gensets. By using the energy storagesystem to supplement power generated by the gensets during high loaddemand and storing excess power generated by the gensets during lowdemand, the gensets can be operated more frequently within an efficientrange of operating conditions. Further, in some embodiments, smaller,more efficient, less expensive gensets may be used to drive a particularload or loads, and the energy storage system can be used to help meethigh demand conditions by reducing required surge capacity or spinningreserve needs, rather than using larger, less efficient, more expensivegensets to meet the need.

In some embodiments, the energy storage system may control operation ofone or more of the gensets. For example, the energy storage system maybe configured to generate and transmit signals to the gensets configuredto control a state of the gensets (e.g., activate and/or deactivate thegensets) or may be one member of a masterless network ofself-coordinating gensets (also known as masterless load demand, orMLD). The energy storage system may monitor network power conditions,and may activate and/or deactivate gensets in the network in order tomeet varying load demand. By deactivating gensets when not needed tomeet demand and/or utilizing excess energy previously stored in theenergy storage system, the energy storage system reduces overallruntime, and fuel consumption, of the gensets. In some embodiments, theenergy storage system may prevent fast cycling and only change a stateof a genset if the energy storage system estimates the power demand canbe met under the changed configuration for at least a threshold amountof time.

In some embodiments, the energy storage system may be configured toreduce transients seen by one or more of the gensets. Transients arecaused by rapid increases or decreases in load demand. In the event of arapid increase in demand, the energy storage system may stop chargingand ramp up power output to supplement power generated by the gensets tohelp prevent or reduce a reduction in power quality (e.g., outputvoltage). In the event of a rapid decrease in demand, the energy storagesystem may absorb excess power from gensets to prevent pole slippageand/or spikes in output voltage (e.g., grid voltage). This may alsoallow the gensets to react to demand change gradually and lower the wearand stress incurred. In one embodiment, the change in genset output canbe changed gradually, such as by a predetermined change time constantrate. This rate can be selected to avoid or reduce human perception(which is tuned to notice sudden changes), thus making the gensets moreacceptable in urban or crowded environments. In yet other embodiments,the AC paralleling energy storage system can take an initial load demandfor a standby, critical, or emergency power system when the primarypower feed fails, allowing a standby genset to start and come up tospeed gradually to take the load. This reduces wear on the standbygenset and can allow use of lower cost gensets that could not otherwisestart up and take the load in the time required.

Referring to FIG. 1, a hybrid generator system 100 including an energystorage system 105 and one or more generator sets (gensets) 110 is shownaccording to an exemplary embodiment. In the illustrated embodiment,genset 110 includes an engine 115 coupled to an alternator 120. Engine115 may be any type of machine configured to convert energy, such asfuel, into mechanical energy (e.g., motion). Engine 115 may be aninternal combustion engine, such as a diesel engine. Alternator 120 maybe any type of machine configured to convert mechanical energy intoelectrical energy, such as an alternating current. In some embodiments,genset 110 may include different and/or additional components thanengine 115 and alternator 120 (e.g., a hydraulically powered generatordriven using hydraulic fluid). Genset 110 may be a mastered ormasterless system (e.g., a masterless load demand genset system or amastered paralleled genset system). While FIG. 1 illustrates a singleenergy storage system 105 connected in parallel with a genset 110 andtwo additional, optional gensets 110, it should be understood that anynumber of energy storage systems and any number of gensets may beutilized.

Energy storage system 105 is configured to provide power to supplementthe power generated by genset 110 to drive load 130 (e.g., in periods ofhigh demand) and store excess power generated by genset 110 (e.g., inperiods of low demand). Energy storage system 105 can operate inparallel with genset 110 to meet larger load demand than genset 110would be capable of supporting on its own. In some embodiments, energystorage system 105 can operate on its own for at least a period of timeto supply light loads without genset 110. Energy storage system 105 maybe configured to charge an energy storage device of energy storagesystem 105 in a manner such that genset 110 is maintained operating in afuel efficient operating range when external system demand/loaddecreases, storing the excess power (e.g., rather than operating genset110 at an operating point above or below an efficient range to chargethe energy storage device). Alternatively, energy storage system 105 maybe configured to source power onto the parallel AC connection whenexternal system demand/load increases (and discharge an energy storagedevice of energy storage system 105) such that genset 110 is maintainedoperating in a fuel efficient operating range, rather than increasegenset 110 output into an inefficient operating range to service theincreased load. Energy storage system 105 may also serve to provide asurge capacity, and may supply power immediately, or nearly immediately,upon sudden frequency dips or voltage drops (e.g., in the case of “dumb”loads, or loads that do not provide information about when changes inload demand will occur in advance of the changes). In some embodiments,energy storage system 105 may act as a “smart” load, and may alertgenset 110 that it will load the system to allow genset 110 to spool upor preload the system to increase the effective spinning reservecapacity in anticipation of large loads suddenly coming online. Energystorage system 105 may store excess power generated until the increasedload appears.

AC paralleled energy storage system 105 may operate as an independentmodule that adds energy storage capacity to genset 110. In someembodiments, the AC paralleled energy storage system 105 may be added toan existing genset 110 or coupled paralleled to the grid serviced by thegenset 110 to convert genset 110 into a hybrid generator system bysourcing to or charging from the paralleled AC output/grid. Energystorage system 105 may have an interface (e.g., control interface,network connection, etc.) through which energy storage system 105 maycommunicate with genset 110 (e.g., receive signals from and/or transmitsignals to genset 110). In some embodiments, during operation, energystorage system 105 may act or appear to the power generation system orfellow co-paralleled gensets as a genset without a governor response(e.g., allowing for instantaneous or near-instantaneous response tochanging load demand). Energy storage system 105 may transmit signals togenset 110 indicating to genset 110 that energy storage system 105should be treated by genset 110 as if it was a genset itself. This mayallow energy storage system 105 to be connected in a “plug-and-play”manner, with little or no modification to genset 110, which may be aconventional synchronous genset or a variable speed genset. In someembodiments, the AC paralleled energy storage system 105 may allow anygenset that can be coupled in parallel with the energy storage system105 to act as a hybrid generator system or as a smart hybrid system ifcommunication interfaces are available to allow coordination.

FIG. 2 shows a more detailed exemplary implementation of energy storagesystem 105. In the illustrated implementation, energy storage system 105includes an energy storage device 205. Energy storage device 205 may be,or include, any type of device capable of storing electrical energy,such as one or more batteries, one or more capacitors (e.g.,ultracapacitors), etc. Energy storage system 105 also includes aninverter 240 configured to transmit power to and/or receive power fromone or more gensets 110, one or more loads 130, and/or one or more powertransmission lines configured to transmit power between genset(s) 110and load(s) 130. Inverter 240 may be a bidirectional inverter configuredto bi-directionally transmit power between energy storage device 205 andgenset(s) 110 and/or load(s) 130. For example, inverter 240 can transmitpower stored in energy storage device 205 to help drive load(s) 130, andinverter can store excess power generated by genset(s) 110 in energystorage device 205. In some embodiments, inverter 240 may be a one-wayinverter, and energy storage system 105 may further include a rectifierand/or DC-DC converter to provide power flow in the other direction.

In some embodiments, energy storage system 105 may include multipleinputs and/or outputs (e.g., power inputs/outputs). For example, energystorage system 105 may include an alternating current (AC) inputconfigured to receive AC power from an external source (e.g., a powergrid) and store the power in energy storage device 205 and/or transmitthe power to load(s) 130 via inverter 240. In some embodiments, the ACpower may be received and transmitted to a DC bus of energy storagesystem 105 (e.g., via an AC-DC converter of energy storage system 105).In one such embodiment, energy storage system 105 may provide power griddistribution and isolation via the AC input, such as by breaking upand/or isolating portions of a local grid by receiving AC power at theAC input, transmitting the power to the DC bus of energy storage system105, and outputting AC power through inverter 240. Alternatively, twoenergy storage devices 105, each with single bi-directional inverters240, can be placed back to back, one on a first grid and one on a secondgrid and coupled to share power via their DC buses. This may helpincrease fault tolerance, simplify and/or reduce power cabling, providelocal surge protection (e.g., via energy storage device 205), and/orprovide resilience against damage (e.g., for military/combatapplications).

Energy storage system 105 may additionally, or alternatively, include adirect current (DC) input. The DC input may allow for DC bus parallelingusing the internal DC bus of energy storage system 105 and connectionsto other DC buses (e.g., operating with other energy storage systemsand/or gensets, such as variable speed gensets, with an interim DC bus).In some embodiments, the other DC buses may have similar voltage to theDC bus of energy storage system 105. In other embodiments, the other DCbuses may have a different voltage, and energy storage system 105 mayinclude a DC-DC converter to convert the voltage of the input power tothe internal DC bus voltage.

The AC and/or DC inputs may be used to take power input from an externalsource (e.g., a dirty or noisy source, such as a noisy, voltage orfrequency-instable grid or weak grid, or unreliable renewable sources,such as wind or solar) and clean up the power. The clean power can bere-emitted on an isolated local grid through inverter 240. This mayenable further fuel savings in systems where local standby gensets wouldnormally be triggered to provide power when the local grid isdisconnected from a weak or unstable utility grid. Excess power can bestored in energy storage device 205, and insufficient power can besupplemented using energy stored in energy storage device 205. Inverter240 may be used to perform power factor correction on a local grid.Thus, energy storage system 105 may be used to support weak local grids,such as at the end of a long transmission line, or subject to localbrown outs, sourcing power as needed and recharging when power is strongagain on the grid.

In some embodiments, energy storage system 105 may input power from oneor more external energy sources 250 using the AC and/or DC inputs. Forexample, input power may be received from one or more external energysources (e.g., renewable energy sources), such as photovoltaic-poweredsources, solar-powered sources, wind-powered sources, solid oxide fuelcells, PEM fuel cells, geo-powered sources, thermal-powered sources,electric-powered sources, etc. In one exemplary implementation, energystorage system 105 may include a DC-DC converter configured to receivepower input from energy source(s) 250 and convert a voltage of the powerinput to a voltage of the internal DC bus of energy storage system 105.Power from external energy source(s) 250 may be stored in energy storagedevice 205 and/or transmitted to load(s) 130, and may be used tosupplement power on a local grid. DC paralleling with additional ACparalleling energy storage systems 105, or “dumb” energystorage/production systems (such as battery packs, fast storagecapacitor banks, or fuel cells), or the internal DC buses of variablespeed gensets. DC paralleling can also be used to wear level andcondition battery systems between multiple energy storage systems 105.

Energy storage system 105 further includes a controller 210 configuredto control operation of inverter 240. Controller 210 may include aprocessor 215, which may be any type of general purpose or specialpurpose processor (e.g., FPGA, CPLD, ASIC, etc.). Controller 210 mayalso include a memory 220, which may include any type of computer ormachine-readable storage medium (e.g., RAM, ROM, PROM, magnetic storage,optical storage, flash storage, etc.). In some embodiments, controller210 may include an input/output (I/O) module or other control interfacethrough which controller 210 can communicate with other components(e.g., receive data from and/or transmit data and/or control signals toother components, such as genset(s) 110).

Controller 210 may include one or more modules configured to implementone or more functions of controller 210. In some embodiments, themodules may be implemented as computer or machine-readable instructionsstored in memory 220 that are executable by processor 215 to perform thefunctions. In some embodiments, the modules may additionally oralternatively be implemented, in whole or in part, via hardware modules(e.g., integrated circuits).

In the illustrated embodiment, controller 210 includes an invertercontrol module 225. Inverter control module 225 is configured to controlan operational state of inverter 240. Module 225 may control the stateof inverter 240 based on operational characteristics of genset(s) 110and/or load(s) 130, for example. In some embodiments, module 225 maycause inverter 240 to change states in response to detecting a change ina power demand of the load. For example, if module 225 detects anincrease in load demand, module 225 may cause inverter 240 to transmitpower from energy storage device 205 to load(s) 130 to supplement powergenerated by genset(s) 110 to meet the demand. If module 225 detects adecrease in load demand, module 225 may cause inverter 240 to receivepower from genset(s) 110 and store the power in energy storage device205. Module 225 may also monitor a state of charge of energy storagedevice 205 and control inverter 240 to receive power from genset(s) 110in response to detecting a low charge condition (e.g., a charge below athreshold charge level). In some embodiments, module 225 may controlinverter 240 based on operational characteristics of genset(s) 110and/or load(s) 130 to maintain genset(s) 110 within a range of operatingconditions (e.g., an efficient operating range).

Power monitoring module 230 is configured to monitor a power state ofgenset(s) 110 and/or the power network/grid. Power monitoring module 230may monitor the power capacity of the network to determine whether toactivate or deactivate one or more paralleled companion gensets. If moregensets are running than needed to meet load demand (i.e., excess powergeneration capacity is online), module 230 may generate and transmit acontrol signal to one or more of the gensets configured to cause thegensets to deactivate (e.g., power down, enter a low-power sleep state,etc.) if the energy storage system 105 is fully or sufficiently chargedand provide any missing power demand from the energy storage system 105.Alternatively, if energy storage system 105 is not at a full orsufficiently high state of charge, it can absorb the excess powergeneration capacity to charge itself and keep the operating gensets intheir most efficient operation ranges. Once fully or sufficientlycharged, the energy storage system 105 can cycle off the excessgensets/capacity off and provide the remaining power demand from itsstorage. If energy storage system 105 and a set of zero or morecurrently active gensets are insufficient to meet load demand, module230 may activate (e.g., power up, wake from a low-power sleep state,etc.) one or more gensets to help meet the demand. In some embodiments,module 230 may attempt to activate a minimum number of gensets needed tomeet the load demand to help reduce fuel consumption and increaseefficiency of the system.

Transient control module 235 is configured to control energy storagesystem 105 to help reduce transients seen by genset(s) 110. For example,in the event of a large load step (e.g., a rapid increase in loaddemand, such as an amount or rate increase above a threshold), transientcontrol module 235 may control inverter 240 to stop charging energystorage device 205, if energy storage device 205 is currently beingcharged, and ramp power output up from energy storage device 205 throughinverter 240 to help meet the increased demand. In some embodiments,module 235 may control inverter 240 to temporarily increase a commandedcharge/discharge rate to help account for rapid increases/decreases inload demand. Module 235 may be configured to help reduce the transientsseen by genset(s) 110 in the event of such rapid changes in load demandand help maintain power quality (e.g., avoid substantial spikes or dipsin voltage provided by genset(s) 110). The energy storage system 105 mayoptionally have one or more local energy storage subsystems eitherinternally or externally coupled to it. These local energy storagesubsystems may have differing voltage levels, rates of charge/discharge,storage capacity, charge/discharge lifetime limits, operatingtemperature limits, etc. In one example embodiment, a super capacitorsubsystem is coupled to the energy storage system 105 and configured tohandle surge demands and rapid charge/discharge demand transients, whileother storage subsystems are utilized for longer durationcharge/discharge cycles. In some embodiments, module 235 may use thesurge capacity of energy storage system 105 to reduce transients, forexample, supporting surges to allow matching (e.g., exact “right-size”matching) of genset capacity to expected load (e.g., average expectedload) and supporting sudden increases in load in a surge capacity untilother gensets can be brought online or a genset system started upon lossof utility grid power (e.g., acting as an uninterruptible power supply,or UPS) and/or absorbing excess power from other gensets in sudden loaddecreases (e.g., to prevent pole slippage, or to support grid codecompliance by absorbing power to allow low voltage event ride through).

FIG. 3 illustrates a flow diagram of a process 300 for controlling anenergy storage system according to an exemplary embodiment. Process 300may be executed by controller 210 of system 200 (e.g., by invertercontrol module 225).

Referring to both FIGS. 2 and 3, controller 210 receives one or moresignals from one or more generator sets communicatively coupled (e.g.,through wired or wireless communication interfaces) to controller 210(305). The signals may be indicative of, or related to, one or moreoperating conditions of one or more gensets 110 and/or one or more loads130. For example, the signals may indicate a rotational velocity (e.g.,RPM), fuel consumption, temperature, power output, voltage, current,frequency, operating time, and/or other operating conditions ofgenset(s) 110. Controller 210 is configured to monitor one or moreoperating conditions of genset(s) 110 and/or load(s) 130 (310).Controller 210 may monitor the operating conditions based on thereceived signals.

Controller 210 is configured to control inverter 240 to store power(e.g., excess power) generated by genset(s) 110 and/or transmit storedpower to drive load(s) 130 based on the monitored operating conditions(315). Controller 210 may control inverter 240 to maintain one or moreof genset(s) 110 within a range of the operating conditions. Forexample, each genset 110 may have a particular range of one or moreoperating conditions, such as an engine RPM range, in which the genset110 operates most efficiently (e.g., uses a lowest amount of fuel).Controller 210 may monitor the RPM or torque output condition of theengine and control inverter 240 to receive excess power generated bygenset(s) 110 and/or supplement power generated by genset(s) 110 to meetdemand of load(s) 130 while maintaining genset(s) 110 within theefficient RPM or torque output range of the engine(s) (e.g., rather thanallowing genset(s) 110 to operate the engine above or below theefficient range to meet the load demand). In some embodiments,controller 210 may be provided with data from which controller 210determines the range of operating conditions (e.g., efficient range) foreach genset 110 (e.g., configuration data). In some embodiments,controller 210 may observe one or more operating parameters (e.g., fueluse data) from genset(s) 110, and may infer the desired range ofoperating conditions through observation of the parameters over one ormore operating cycles.

In some embodiments, controller 210 may be configured to change anoperational state of inverter 240 based on changes in load power demand,such as by comparing changes in load demand to a threshold level. Forexample, controller 210 may monitor a load demand and determine whetherthe demand increases or decreases above a threshold level (e.g., whetherthe amount of demand or rate of increase/decrease exceeds a thresholdlevel). In response to the change exceeding the threshold, controller210 may change an operational state of inverter 240 (e.g., change adirection of current flow through inverter 240 and/or increase ordecrease a charge/discharge rate).

Controller 210 may detect an increase in power demand above a thresholdincrease. For example, controller 210 may detect an amount of powerdemand (e.g., in kilowatts, or kW) increase above a threshold increaseamount and/or a rate increase above a threshold rate (e.g., indicating arapid increase in load demand). In response, controller 210 may controlinverter 240 to discharge power stored in energy storage device 205 todrive load(s) 130. In some embodiments, controller 210 may control anamount or rate of discharge based in part on the power demand and/orother operating parameters of genset(s) 110 and/or load(s) 130 (e.g., tomaintain genset(s) 110 within a range of the operating conditions andprevent genset(s) 110 from operating outside of the desired range tomeet the increased demand).

Controller 210 may detect a decrease in power demand above a thresholddecrease. For example, controller 210 may detect an amount of powerdemand decrease above a threshold decrease amount and/or a rate decreaseabove a threshold rate (e.g., indicating a rapid drop in load demand).In response, controller 210 may control inverter 240 to charge energystorage device 205 using power generated by genset(s) 110 in excess ofthe load demand. In some embodiments, controller 210 may control anamount or rate of charge based in part on the power demand and/or otheroperating parameters of genset(s) 110 and/or load(s) 130 (e.g., tomaintain genset(s) 110 within a range of the operating conditions andprevent genset(s) 110 from operating outside of the desired range toadjust to the decreased load demand).

In some embodiments, controller 210 may generate control signalsconfigured to cause genset(s) 110 to change an operating state. Forexample, controller 210 may transmit control signals to one or moregenset(s) to cause them to activate or deactivate to meet changes inload demand while reducing fuel consumption of the overall generatorsystem. Controller 210 may control inverter 240 to charge energy storagedevice 205 with excess power generated by genset(s) 110 while genset(s)110 operate within a range of operating conditions. Controller 210 maygenerate control signals configured to cause one or more genset(s) 110to deactivate, for example, in response to determining that load demandcan be met without all genset(s) 110 active and/or a current powergenerated by the active genset(s) 110 within the range of operatingconditions exceeding load demand by a greater amount or rate than can bestored in energy storage device 205 (e.g., such that one or moregenset(s) 110 would be operated outside of the desired range ofoperating conditions to adjust to the lower demand, if all genset(s) 110remained active).

Controller 210 may control inverter 240 to discharge power from energystorage device 205 to drive load(s) 130. Controller 210 may generatecontrol signals configured to cause one or more genset(s) 110 toactivate to help drive load(s) 130, for example, if the combinedcapacity of the currently active genset(s) 110 and energy storage system105 is insufficient to meet load demand. Controller 210 may generatecontrol signals configured to cause one or more genset(s) to deactivatewhile energy storage system 105 is helping drive load(s) 130, in someembodiments. For example, if controller 210 determines load demand canbe met using power stored in energy storage device 205 and a lessernumber of genset(s) 110 than are currently active, controller 210 maydeactivate one or more genset(s) 110 to conserve fuel and/or allow theremaining genset(s) 110 to operate in the desired range of operatingconditions.

FIG. 4 is a state diagram 400 of an energy storage system control schemeaccording to an exemplary embodiment. State diagram 400 may be utilizedby controller 210 (e.g., inverter control module 225) to controloperation of inverter 240. In some embodiments, controller 210 may beconfigured to increase or decrease its priority in the paralleled systemof genset(s) 110 to allow it to preempt other gensets when it is fullycharged or in need of charging.

Referring to both FIGS. 2 and 4, controller 210 may start operation(405) in a constant voltage state 410. In some embodiments, a start mayoccur with a low or minimal load 130 attached to genset(s) 110. Inconstant voltage state 410, controller 210 may control inverter 240 todischarge power stored in energy storage device 205 at a substantiallyconstant voltage (e.g., a voltage level within a threshold distance of,or range around, a set output voltage value). Once a genset 110 starts(e.g., is activated), controller 210 determines whether to transitioninverter 240 to either a charge state 465 or a constant current state420. If a genset 110 starts and energy storage device 205 is in a lowcharge state (e.g., a state of charge, or SOC, of energy storage device205 is below a threshold value) (430), controller 210 transitionsinverter 240 to charge state 465. In charge state 465, power generatedby the active genset(s) 110 is used to charge energy storage device 205.In some embodiments, charging may be limited by a maximum power (e.g.,maximum AC power) setting.

If a genset 110 starts and energy storage device 205 is not in a lowcharge state (425), controller 210 transitions inverter 240 to constantcurrent state 420. In constant current state 420, inverter 240 iscontrolled to discharge power from energy storage device 205 to maintaina substantially constant current (e.g., a current level within athreshold distance of, or range around, a set output current value). Ifone or more active genset(s) 110 are capable of meeting load demand(e.g., within an efficient operating range of genset(s) 110) (435),controller 210 may ramp down a current output of energy storage device205 (440). Controller 210 may place energy storage system 105 in an offstate 450. In off state 450, inverter 240 is controlled such that powerdoes not flow to or from energy storage device 205. Controller 210continues receiving operating condition data and monitoring load demandand/or operation of genset(s) 110. If load demand increases (445),controller 210 may return energy storage system 105 to constant currentstate 420. If energy storage device 205 enters a low state of chargewhile in constant current state 420 (470), controller 210 may transitionenergy storage system 105 into charge state 465.

While in off state 450, if controller 210 detects a decrease in loaddemand and a state of charge of energy storage device 205 that is lessthan full or under a threshold charge level, or detects that there isavailable capacity in excess of load demand and energy storage device205 is in a charge region (e.g., a state of charge range in which energystorage device 205 is permitted to charge) (455), controller 210 maytransition energy storage system 105 to charge state 465. If load demandincreases while in charge state 465 and/or the state of charge of energystorage device 205 is at or above a maximum charge level (e.g., energystorage device 205 is full) (460), controller 210 may transition energystorage system 105 to off state 450. In some embodiments, controller 210may transition energy storage system to constant current state 420 tomeet the increased load demand. In the illustrated embodiment, in any ofconstant current state 420, off state 450, or charge state 465, if alast active genset 110 is deactivated (e.g., by command of controller210 or by emergency shutdown conditions, such as a failure of the genset110) (415), controller 210 may transition energy storage system 105 toconstant voltage state 410.

FIG. 5 is a flow diagram of a process 500 for controlling network powerusing an energy storage system according to an exemplary embodiment.Process 500 may be executed by controller 210 (e.g., power monitoringmodule 230) to control operating states (e.g. activation and/ordeactivation) of one or more gensets 110. For example, process 500 maybe used to keep a low (e.g., minimum) number of gensets 110 active tomeet current load demand, while preventing fast cycling and avoidingpushing the system into a state it is incapable of maintaining for atleast a threshold amount of time (e.g., threshold number of minutes). Insome embodiments, process 500 may be used (e.g., in combination withprocess 600, described below) to help ensure there is sufficientcapacity to allow energy storage system 105 to help provide transientsupport.

Referring to both FIGS. 2 and 5, controller 210 may sum a total capacityof the current online gensets 110 and energy storage device 205 (505).Controller 210 may determine or estimate the current capacity of eachgenset 110 and/or a combination of multiple gensets 110 based on signalsreceived from the gensets 110.

Controller 210 may determine (e.g., calculate) a next turn on threshold(e.g., in kW) (510). The next turn on threshold may be a threshold levelpast which (e.g., below which) an inactive genset 110 may be activatedto help meet load demand. In some embodiments, the next turn onthreshold may be a user configurable threshold value, such as a percentof total network power or a fixed amount of power (e.g., in kW).

Controller 210 determines if the network power (e.g., total capacity) isover the next turn on threshold (e.g., if the total capacity is belowthe threshold level) (515). If so, controller 210 calculates how longthe system (e.g., energy storage system 105) could maintain the currentpower level of the system (520). If the time for which the power levelis expected to be maintained below the threshold exceeds a cycling timethreshold (525), an inactive genset 110 may be activated, and the poweroutput control may be set by controller 210 to a current amount over thenext turn on threshold (plus, in some embodiments, a measurement error)(530).

If the network power is not over the next turn on threshold, controller210 calculates the next turn off threshold (535). The turn off thresholdmay be a threshold level past which (e.g., above which) an active genset110 may be deactivated (e.g., in the occurrence of a low load demand).In some embodiments, the next turn off threshold may be a userconfigurable threshold value, such as a percent of total network poweror a fixed amount of power (e.g., in kW).

Controller 210 determines if the network power is over the next turn offthreshold (540). If so, controller 210 determines how long the system(e.g., energy storage system 105) could maintain the current power levelof the system (545). If the time for which the power level is expectedto be maintained past the threshold exceeds a cycling time threshold(550), controller 210 determines if deactivating a genset 110 willresult in enough capacity (e.g., energy storage device 205 capacity) tohold a largest predicted transient for at least a threshold amount oftime (e.g., 30 seconds) (555). If not, controller 210 may not deactivatea genset 110. If so, and the genset 110 considered for deactivation isnot a last active genset 110, controller 210 may deactivate a genset 110and set a power output control to an amount over the next turn offthreshold (plus, in some embodiments, a measurement error) (560). If thegenset 110 considered for deactivation is the last active genset 110,controller 210 may transition energy storage system 105 to a voltagecontrol (e.g., constant voltage) mode (565).

FIG. 6 is a flow diagram of a process 600 for controlling transientsusing an energy storage system according to an exemplary embodiment.Process 600 may be executed by controller 210 (e.g., transient controlmodule 235) to control inverter 240 to help reduce transients seen atgenset(s) 110. In some embodiments, process 600 may be utilized if loaddemand has changed by greater than a threshold amount or rate.

Referring to FIGS. 2 and 6, controller 210 may determine an amount(e.g., relative amount) of power demand change (605). In someembodiments, the amount of change may be calculated as the networkcapability multiplied by the percentage of change in demand. In someembodiments, the amount may be an absolute power change (e.g., in kW).Controller 210 may adjust a maximum charge/discharge rate of energystorage system 105 based on the determined amount of change (610). Forexample, controller 210 may increase the discharge rate based on thedetermined amount to meet a rapid increase in load demand and/or mayincrease the charge rate based on the determined amount to meet a rapiddecrease in demand. In some embodiments, the adjusted rate may be higherthan a normal maximum charge/discharge rate used during normal (e.g.,non-rapid) changes in load demand. If the discharge rate would gonegative, controller 210 may set the discharge rate to zero (615).Controller 210 may calculate a final power that inverter 240 wouldprovide (e.g., steady state), and may adjust operation of inverter 240to ramp up/down to that final power level (620). In some embodiments, ifthe charge rate would go negative, and the state of charge of energystorage device 205 is above a threshold state of charge, controller 210may transition energy storage system 105 to a current control state(e.g., constant current state).

In some embodiments, an energy storage system such as energy storagesystem 105 may be utilized in a multiple-phase implementation to helpmonitor and balance loading on the phases. Generator sets or alternatorscan have an unbalanced load attached to them. For example, a three phasealternator can have a heavy load on one or two of the phases and a lightload on the third, or a heavy load on one phase and light load on theother two phases, and so on. This can lead to higher neutral linecurrents and heating, and can additionally lower power quality becauseof the voltage imbalance between phases. In other situations, a load onone or two phases could also be unbalanced by having the load demand onthe phase exceed the phase's continuous or surge capacity, potentiallycausing system de-rate or shutdown, but yet not have the overall loadexceed the total generator set/alternator output rating.

In some systems, active filtering is used with inverters and other powerelectronic controls to sense the local grid and condition and smooth thepower on it via feedback control on the inverter. However, while activefiltering will smooth out the power seen on the local grid, it will notfully balance the load on an unbalanced generator set or alternatorfeeding power in to the local grid, or if it does help load balance itwill be as a secondary result of power smoothing, and will not bemaintained for very long.

Referring now to FIG. 7, a block diagram of a multiple-phase hybridgenerator system including an energy storage system 105 configured tohelp balance loading across phases is shown according to an exemplaryembodiment. Energy storage system 105 can include components similar toany or all of the components shown in FIG. 2, such as inverter controlmodule 225, power monitoring module 230, transient control module 235,and bidirectional inverter 240. In some embodiments, components commonto FIGS. 2 and 7 may include the same or similar features as describedabove with respect to FIG. 2.

In the implementation illustrated in FIG. 7, energy storage system 105includes a load balancing module 715. Load balancing module 715 isconfigured to determine a load condition on one or more of the phasesover which generator set(s) 110 transmit power to drive load(s) 130.Load balancing module 715 is configured to detect a load imbalance onone or more of the phases. In some embodiments, load balancing module715 may work alone or in conjunction with power monitoring module 230 tomonitor load conditions on the phases. In some embodiments, loadbalancing module 715 may monitor a voltage of the phases and monitorload conditions and/or detect imbalances based on the voltage. In someembodiments, energy storage system 105 may receive current signals fromone or more current sensors 710 (e.g., clamp-style sensors, in-linesensors, etc.) configured to monitor current flowing through one or morephases, and load balancing module 715 may monitor load conditions and/ordetect imbalances in load using the current signals.

Load balancing module 715 is configured to control inverter 240 to storepower from generator set(s) 110 and/or transmit stored power to helpdrive load(s) 130 in response to the imbalance. In some embodiments,inverter 240 may include separate single-phase inverters 705 for each ofthe phases. Each single-phase inverter 705 controls a flow of power intoand out of energy storage device 205 for a single phase. Load balancingmodule 715 can independently control flow of power into and out ofenergy storage device 205 by controlling single-phase inverters 705(e.g., via separate control signals transmitted to single-phaseinverters 705). In some embodiments, each single-phase inverter 705 maybe coupled to one or more secondary energy storage devices (e.g., one ormore batteries or one or more capacitors/supercapacitors) configured totemporarily store power transmitted from energy storage device 205before transmitting the power to help power a heavily loaded phase.

Load balancing module 715 can be used to balance the load on thegenerator set/alternator phases and store the excess power of apreviously unloaded phase in energy storage device 205. This storedpower could then be used to provide spinning reserve, surge fill in, orallow generator set(s) 110 to turn off under light load or inefficientoperating conditions, such that power for load(s) 130 can be provided byenergy storage system 105. Under high, yet unbalanced load conditions,energy storage system 105 could provide the extra power demanded to keepthe heavily loaded phases from getting overheated or exceeding thealternator damage curve. This extra power could come from energy storedin energy storage device 205 and/or from pulling and transferring powerfrom the more lightly loaded phases. For power transfer, power could bestored temporarily (e.g., by energy storage devices coupled tosingle-phase inverters 705) before being reconverted and pushed on tothe heavy demand phases. In some embodiments, pure power electronicsphase to phase direct conversion could be used.

Because the electricity flows in a fungible manner, energy storagesystem 105 need not be an integral part of generator set(s) 110, andcould be a separate standalone unit. In some embodiments, energy storagesystem 105 could be used as an add on to pre-existing generator sets orparalleled generator set farms of any origin, and they or their controlsystems would not necessarily need to know how energy storage system 105operates or even be able to communicate with energy storage system 105to still benefit. In some such situations, load balancing module 715could determine that the local power load is unbalanced and thecorrection needed (e.g., via current sensors 710 and/or by monitoringthe voltage differences in the phases. Other power factors could also beconsidered and incorporated, such as harmonics and power factor, etc. Acorrection could be applied to the grid using a feedback loop until thecurrents balance (e.g., within a threshold level of one another) or thevoltage differences or other bad load characteristics are reduced oreliminated.

In some embodiments, load balancing module 715 may determine and utilizeone or more characteristics of generator set(s) 110 in controllingoperation of inverter 240. If, for example, the alternatorcharacteristics of generator set(s) were known, such as the generatordamage curve, load balancing module 715 can utilize this information incombination with the load condition information to control flow of powerto and from energy storage device 205 to store excess power and/or helpdrive load(s) 130 on one or more phases. This may allow energy storagesystem 105 to better manage generator set(s) 110/alternator loading,such as by engage in phase peak shaving to prevent individual phasesfrom becoming overloaded under high unbalanced load conditions. Furthercommunications with the associated genset(s) (e.g., through a centralcontroller or via a masterless load demand control (MLD) where energystorage system 105 could appear as just another generator set) couldallow for increased coordination and efficiencies (e.g., when dealingwith a generator set farm with differing sized generator sets that canbe switched on and off to meet load demand).

In some implementations, energy storage system 105 can be used withsmall generator set installations, particularly multiple generator setsites such as with military applications. Energy storage system 105 mayprovide automatic balancing of phases that generally will see varyingand ad hoc load demands in such applications. Load balancing can providean improved benefit for smaller alternators (e.g., due to magnitude ofphase differences likely to be seen). In addition, power scavenged byphase balancing can be put to use in fuel savings with AC paralleling,as described above.

In some implementations, a utility grid connection feeding power onto alocal power grid could have a weak phase or an unbalanced load demandupstream from the local power grid, leading to unstable power or localbrown outs on select phases, yet may still be delivering the power beingdemanded. Some utilities charge power quality tariffs to users, inparticular, industrial/commercial users, for exceptionally bad loads.Energy storage system 105 could pull power from the good phases and pushit onto the weak phase, as noted above for the heavily loaded genset(e.g., using direct phase to phase conversion or a local supercapacitoror other temporary storage). In these embodiments it is noted that theenergy storage system 105 and load balancing module 715 can be pairedwith one or more generators, or installed as a standalone system tobalance and correct the local grid supply or local loads.

In some embodiments, energy storage system 105 could be configured totransmit a signal to a transfer switch configured to disconnect one ormore phases of a power grid to which a local power grid is connected(e.g., a larger utility grid) in response to the signal. The transferswitch can disconnect a weak phase, and energy storage system 105 canutilize power stored in energy storage device 205 and/or powertransferred from other, stronger phases to power the weak phase. In thismanner, energy storage system 105 can recreate the weak phase internallyon the local power grid to supply power demand that would otherwise notbe met by the weak phase when connected to the utility grid. Longer termstorage could also be used to charge local UPS-style battery storagefrom a utility grid seeing an off balanced local load, balancing theload seen by the utility grid and charging the battery/storage from theweakly loaded phase so that the charging of the battery is not seen bylocal users. This local inverter/battery could also then be used asabove to provide local peak shaving, spinning reserve, surge supply,fill in, or individual phase high load balancing/phase fill in. Powerfactor correction, harmonic correction, and other active filtering powerconditioning could also be provided.

In situations where electric vehicles or plug-in hybrids, or buses, or afleet of local removable batteries need to be charged (such as forelectric forklifts, or electric delivery vehicles) or large localstorage is charged for peak shaving/grid fill in, energy storage system105 could be used to balance the load on the grid. In some embodiments,energy storage system 105 could charge the batteries/storage by onlyloading the relatively unloaded phases or by “filling in” the loads oneach phase to a selected nominal average or maximum load level. In thismanner, the local load is managed so the local system is not stressedcharging the associated batteries/storage units, and the local loads andusers do not experience power sag or phase brown outs. At the same time,a well-balanced load is presented to the utility connection, avoidingpower quality tariffs. In effect, a virtual “off-peak” charging systemis created that utilizes the power pulled from filling in the load onlow utilized phases and yet also dynamically load balances and preventsoverload on the local grid. In some embodiments, this large bank ofremovable battery/storage and vehicle batteries can also be used toprovide peak shaving, load surge (such as for large motor start up oraluminum smelting start up), or to sell grid fill in back to the utilityas needed. A user set minimum charge level or minimum set of fullcharged units could be set to allow for continued local use for the mainbattery purpose (such as fork lift usage or fleet vehicles). If vehiclesare hybrids, such as, but not limited to, hybrid cars, buses, ordelivery or other utility vehicles, they could potentially be used toprovide a power source for fill in, or emergency standby powergeneration for the plant/residence either by manual starting or startingunder automatic control of the energy storage system 105.

FIG. 8 illustrates a flow diagram of a process 800 for balancing a loadacross multiple phases using an energy storage system. Referring now toboth FIGS. 7 and 8, energy storage system 105 determines a loadcondition on one or more phases over which generator set(s) 110 providepower to drive load(s) 130. One or more phases may be in a high loadcondition (e.g., have a load higher than a threshold level, or at leasta threshold level above a load level of one or more other phases) or alow load condition (e.g., have a load lower than a threshold level, orat least a threshold level below one or more other phases) with respectto other phases. In some embodiments, energy storage system 105 maydetermine a load condition using a current, voltage, and/or otherinformation associated with a phase. The load condition information isused to detect an imbalance of one or more of the phases.

Energy storage system 105 controls inverter 240 to store power generatedby generator set(s) 110 in energy storage device 205 and/or transmitpower stored in energy storage device 205 to help drive load(s) 130 onone or more phases in response to detecting a load imbalance. Loadbalancing module 715 may detect that a particular phase is in a low loadcondition, and excess power generated on the phase by generator set(s)110 may be stored in energy storage device 205 to load the phase andbalance the phase with the other phases. Load balancing module 715 maydetect that a particular phase is in a high load condition, and energystorage system 105 may transmit power from energy storage device 205 tosupplement power supplied by generator set(s) 110 on the phase to drivethe load(s) 130 on the phase.

The disclosure is described above with reference to drawings. Thesedrawings illustrate certain details of specific embodiments thatimplement the systems and methods and programs of the presentdisclosure. However, describing the disclosure with drawings should notbe construed as imposing on the disclosure any limitations that may bepresent in the drawings. The present disclosure contemplates methods,systems and program products on any machine-readable media foraccomplishing its operations. The embodiments of the present disclosuremay be implemented using an existing computer processor, or by a specialpurpose computer processor incorporated for this or another purpose orby a hardwired system. No claim element herein is to be construed underthe provisions of 35 U.S.C. § 112, sixth paragraph, unless the elementis expressly recited using the phrase “means for.” Furthermore, noelement, component or method step in the present disclosure is intendedto be dedicated to the public, regardless of whether the element,component or method step is explicitly recited in the claims.

As noted above, embodiments within the scope of the present disclosureinclude program products comprising machine-readable storage media forcarrying or having machine-executable instructions or data structuresstored thereon. Such machine-readable storage media can be any availablemedia that can be accessed by a computer or other machine with aprocessor. By way of example, such machine-readable storage media caninclude RAM, ROM, EPROM, EEPROM, CD ROM or other optical disk storage,magnetic disk storage or other magnetic storage devices, or any othermedium which can be used to carry or store desired program code in theform of machine-executable instructions or data structures and which canbe accessed by a computer or other machine with a processor.Combinations of the above are also included within the scope ofmachine-readable storage media. Machine-executable instructions include,for example, instructions and data which cause a computing device ormachine to perform a certain function or group of functions. Machine orcomputer-readable storage media, as referenced herein, do not includetransitory media (i.e., signals in space).

Embodiments of the disclosure are described in the general context ofmethod steps which may be implemented in one embodiment by a programproduct including machine-executable instructions, such as program code,for example, in the form of program modules executed by machines innetworked environments. Generally, program modules include routines,programs, objects, components, data structures, etc., that performparticular tasks or implement particular abstract data types.Machine-executable instructions, associated data structures, and programmodules represent examples of program code for executing steps of themethods disclosed herein. The particular sequence of such executableinstructions or associated data structures represent examples ofcorresponding acts for implementing the functions described in suchsteps.

Embodiments of the present disclosure may be practiced in a networkedenvironment using logical connections to one or more remote computershaving processors. Logical connections may include a local area network(LAN) and a wide area network (WAN) that are presented here by way ofexample and not limitation. Such networking environments are commonplacein office-wide or enterprise-wide computer networks, intranets and theInternet and may use a wide variety of different communicationprotocols. Those skilled in the art will appreciate that such networkcomputing environments will typically encompass many types of computersystem configurations, including personal computers, hand-held devices,multi-processor systems, microprocessor-based or programmable consumerelectronics, network PCs, servers, minicomputers, mainframe computers,and the like. Embodiments of the disclosure may also be practiced indistributed computing environments where tasks are performed by localand remote processing devices that are linked (either by hardwiredlinks, wireless links, or by a combination of hardwired or wirelesslinks) through a communications network. In a distributed computingenvironment, program modules may be located in both local and remotememory storage devices.

An exemplary system for implementing the overall system or portions ofthe disclosure might include a computing device that includes, forexample, a processing unit, a system memory, and a system bus thatcouples various system components including the system memory to theprocessing unit. The system memory may include read only memory (ROM)and random access memory (RAM) or other non-transitory storage medium.The computer may also include a magnetic hard disk drive for readingfrom and writing to a magnetic hard disk, a magnetic disk drive forreading from or writing to a removable magnetic disk, and an opticaldisk drive for reading from or writing to a removable optical disk suchas a CD ROM or other optical media. The drives and their associatedmachine-readable media provide nonvolatile storage of machine-executableinstructions, data structures, program modules, and other data for thecomputer.

It should be noted that although the flowcharts provided herein show aspecific order of method steps, it is understood that the order of thesesteps may differ from what is depicted. Also two or more steps may beperformed concurrently or with partial concurrence. Such variation willdepend on the software and hardware systems chosen and on designerchoice. It is understood that all such variations are within the scopeof the disclosure. Likewise, software and web implementations of thepresent disclosure could be accomplished with standard programmingtechniques with rule based logic and other logic to accomplish thevarious database searching steps, correlation steps, comparison stepsand decision steps. It should also be noted that the word “component” asused herein and in the claims is intended to encompass implementationsusing one or more lines of software code, and/or hardwareimplementations, and/or equipment for receiving manual inputs.

The foregoing description of embodiments of the disclosure have beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the disclosure to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the disclosure. Theembodiments were chosen and described in order to explain the principalsof the disclosure and its practical application to enable one skilled inthe art to utilize the disclosure in various embodiments and withvarious modifications as are suited to the particular use contemplated.

What is claimed is:
 1. An energy storage system comprising: an energystorage device; a bidirectional inverter configured to control a flow ofpower into or out of the energy storage device; and a controllerconfigured to: detect an unbalanced load condition on a plurality ofphases of a local power grid coupled to one or more generator sets, theplurality of phases comprising a first phase and a second phase moreheavily loaded than the first phase, the controller configured tocontrol the bidirectional inverter to at least one of: store power inthe energy storage device from the first phase; or source power from theenergy storage device to the second phase.
 2. The energy storage systemof claim 1, wherein the local power grid is an isolated local powergrid.
 3. The energy storage system of claim 1, wherein the controller isconfigured to control the bidirectional inverter to correct theunbalanced load condition on the one or more generator sets by at leastone of storing power in the energy storage device from the first phaseor sourcing power from the energy storage device to the second phase. 4.The energy storage system of claim 3, wherein the controller isconfigured to control the bidirectional inverter to correct theunbalanced load condition of the plurality of phases coupled to the oneor more generator sets to a selected nominal average.
 5. The energystorage system of claim 3, wherein the controller is configured tocontrol the bidirectional inverter to fill in the unbalanced loadcondition and operate the one or more generator sets in a selected rangeof efficient operating conditions.
 6. The energy storage system of claim3, wherein the controller is configured to control the bidirectionalinverter to correct the unbalanced load condition of the plurality ofphases coupled to the one or more generator sets and operate at leastone of the one or more generator sets below a generator damage curvelimit.
 7. The energy storage system of claim 1, wherein the controlleris configured to generate at least one control signal configured tocontrol an activation and deactivation of at least one of the one ormore generator sets based on a level of power stored in the energystorage system and the unbalanced load condition of the local powergrid.
 8. The energy storage system of claim 1, wherein the controller isconfigured to: receive a plurality of current signals from one or morecurrent sensors, wherein each of the plurality of current signalsindicates a current flow on one of the plurality of phases; and monitorthe unbalanced load condition and detect the load imbalance using thecurrent signals.
 9. The energy storage system of claim 1, wherein thecontroller is configured to: monitor a voltage for each of the pluralityof phases; and monitor the unbalanced load condition and detect the loadimbalance using the voltages for the plurality of phases.
 10. The energystorage system of claim 1, wherein the controller is configured to:determine a characteristic of at least one generator set of the one ormore generator sets; and control the bidirectional inverter to storepower generated by the one or more generator sets in the energy storagedevice and transmit power from the energy storage device to the loadbased on the characteristic of at least one generator set of the one ormore generator sets and the unbalanced load condition and prevent afirst phase output of the at least one generator set from overloading.11. A method of controlling a flow of power to and from an energystorage system, the method comprising: determining, at a controller ofthe energy storage system, a load condition on one or more of aplurality of phases of a local alternating current (AC) grid coupled toone or more generator sets; and controlling a bidirectional inverter ofthe energy storage system to store power from the local AC grid in anenergy storage device of the energy storage system and transmit-powerfrom the energy storage device to a load driven by the one or moregenerator sets on the local AC grid in response to detecting a loadimbalance between the plurality of phases to mitigate the loadimbalance.
 12. The method of claim 11, further comprising independentlycontrolling the flow of power into or out of the energy storage devicefor each of the plurality of phases using the bidirectional inverter.13. The method of claim 11, further comprising: detecting a first phaseof the plurality of phases having a different load than one or moresecond phases of the plurality of phases; and controlling an operationalstate of the bidirectional inverter to store power in or transmit powerfrom the energy storage device via the first phase in response todetecting the different load on the first phase.
 14. The method of claim13, wherein: detecting a lower load on the first phase than on the oneor more second phases; and controlling the bidirectional inverter tocharge the energy storage device with power from the first phase inresponse to detecting the lower load on the first phase to mitigate theload condition on the one or more of a plurality of phases coupled tothe one or more generator sets.
 15. The method of claim 13, wherein:detecting a higher load on the first phase than on the one or moresecond phases; and controlling the bidirectional inverter dischargepower from the energy storage device to drive the load on the firstphase in response to detecting the higher load on the first phase tomitigate the load condition on the one or more of a plurality of phasescoupled to the one or more generator sets.
 16. The method of claim 15,further comprising: determining a characteristic of at least onegenerator set of the one or more generator sets; and controlling thebidirectional inverter to store power generated by one or more generatorsets in the energy storage device and transmit power from the energystorage device to the load based on the characteristic of the at leastone generator set and the load condition and prevent a first phase of aplurality of phases of the at least one generator set from overloading.17. A hybrid generator system comprising: a generator set configured togenerate power to drive a load; and an energy storage system comprising:an energy storage device; a bidirectional inverter configured to controla flow of power into or out of the energy storage device via a pluralityof phases of the generator set; and a controller configured to controlthe bidirectional inverter based on a load condition on one or more ofthe plurality of phases, wherein the controller is configured to controlthe bidirectional inverter to store power generated by the generator setin the energy storage device and transmit power from the energy storagedevice to the load in response to detecting a load imbalance between theplurality of phases of the generator set to correct the load imbalanceon the generator set.
 18. The hybrid generator system of claim 17,wherein controller is further configured to: detect the load imbalanceon the generator set on a first phase of the plurality of phases;provide power on the first phase using power from the energy storagedevice or one or more second phases of the plurality of phases tocorrect the load imbalance on the generator set.
 19. The hybridgenerator system of claim 17, wherein controller is further configuredto: detect the load imbalance on the generator set on a first phase ofthe plurality of phases; store power from one or more second phases tothe energy storage device to correct the load imbalance on the generatorset.
 20. The hybrid generator system of claim 17, wherein thebidirectional inverter is configured to independently control the flowof power into or out of the energy storage device for each of theplurality of phases.
 21. An energy storage system comprising: an energystorage device; a bidirectional inverter configured to control a flow ofpower into or out of the energy storage device via a plurality ofphases; and a controller configured to: detect a load change transienton one or more phases of a plurality of phases of a local power grid andsource power from the energy storage device to one or more loaded phasesof the plurality of phases or store power to the energy storage devicefrom one or more unloaded phases of the plurality of phases to balancethe phases and reduce the load change transient for one or more coupledgensets.
 22. The energy storage system of claim 21, wherein thecontroller is configured to: detect the load change transient on the oneor more phases of the plurality of phases of the local power grid abovea threshold level; and control the bidirectional inverter to sourcepower from the energy storage device to one or more loaded phases of theplurality of phases or store power in the energy storage device from oneor more unloaded phases of the plurality of phases to balance the phasesand reduce the load change transient for the one or more coupledgensets.
 23. The energy storage system of claim 21, wherein thecontroller is configured to: receive a signal indicating a large loadwill be added to one or more phases coming on line the plurality ofphases of the local power grid; and control the bidirectional inverterto store power in the energy storage device from one or more phases ofthe plurality of phases to preload the one or more coupled gensets. 24.The energy storage system of claim 21, wherein the controller isconfigured to: detect the load change transient on the one or morephases of the plurality of phases of the local power grid above athreshold level; and control the bidirectional inverter to source powerfrom the energy storage device to one or more loaded phases of theplurality of phases or store power in the energy storage device from oneor more unloaded phases of the plurality of phases to balance the phasesand reduce human perception of the load change transient on the one ormore coupled gensets.
 25. An energy storage system comprising: an energystorage device; a bidirectional inverter configured to control a flow ofpower into or out of the energy storage device via a plurality ofphases; and a controller configured to: detect a load imbalance on aplurality of phases of a local power grid and control the bidirectionalinverter to balance the plurality of phases by storing power in theenergy storage device from one or more unloaded phases of the pluralityof phases.